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lzw压缩算法的c语言实现

王朝c/c++·作者佚名  2006-01-31
窄屏简体版  字體: |||超大  

1 程序由五个模块组成。

(1) lzw.h 定义了一些基本的数据结构,常量,还有变量的初始化等。

#ifndef __LZW_H__

#define __LZW_H__

//------------------------------------------------------------------------------

#include <stdio.h>

#include <stdlib.h>

#include <windows.h>

#include <memory.h>

//------------------------------------------------------------------------------

#define LZW_BASE 0x102// The code base

#define CODE_LEN 12 // Max code length

#define TABLE_LEN 4099 // It must be prime number and bigger than 2^CODE_LEN=4096.

// Such as 5051 is also ok.

#define BUFFERSIZE 1024

//------------------------------------------------------------------------------

typedef struct

{

HANDLE h_sour; // Source file handle.

HANDLE h_dest; // Destination file handle.

HANDLE h_suffix; // Suffix table handle.

HANDLE h_prefix; // Prefix table handle.

HANDLE h_code; // Code table handle.

LPWORD lp_prefix; // Prefix table head pointer.

LPBYTE lp_suffix; // Suffix table head pointer.

LPWORD lp_code; // Code table head pointer.

WORD code;

WORD prefix;

BYTE suffix;

BYTE cur_code_len; // Current code length.[ used in Dynamic-Code-Length mode ]

}LZW_DATA,*PLZW_DATA;

typedef struct

{

WORD top;

WORD index;

LPBYTE lp_buffer;

HANDLE h_buffer;

BYTE by_left;

DWORD dw_buffer;

BOOL end_flag;

}BUFFER_DATA,*PBUFFER_DATA;

typedef struct //Stack used in decode

{

WORD index;

HANDLE h_stack;

LPBYTE lp_stack;

}STACK_DATA,*PSTACK_DATA;

//------------------------------------------------------------------------------

VOID stack_create( PSTACK_DATA stack )

{

stack->h_stack = GlobalAlloc( GHND , TABLE_LEN*sizeof(BYTE) );

stack->lp_stack = GlobalLock( stack->h_stack );

stack->index = 0;

}

//------------------------------------------------------------------------------

VOID stack_destory( PSTACK_DATA stack )

{

GlobalUnlock( stack->h_stack );

GlobalFree ( stack->h_stack );

}

//------------------------------------------------------------------------------

VOID buffer_create( PBUFFER_DATA buffer )

{

buffer->h_buffer = GlobalAlloc( GHND, BUFFERSIZE*sizeof(BYTE) );

buffer->lp_buffer = GlobalLock( buffer->h_buffer );

buffer->top = 0;

buffer->index = 0;

buffer->by_left = 0;

buffer->dw_buffer = 0;

buffer->end_flag = FALSE;

}

//------------------------------------------------------------------------------

VOID buffer_destory( PBUFFER_DATA buffer )

{

GlobalUnlock( buffer->h_buffer );

GlobalFree ( buffer->h_buffer );

}

//------------------------------------------------------------------------------

VOID re_init_lzw( PLZW_DATA lzw ) //When code table reached its top it should

{ //be reinitialized.

memset( lzw->lp_code, 0xFFFF, TABLE_LEN*sizeof(WORD) );

lzw->code = LZW_BASE;

lzw->cur_code_len = 9;

}

//------------------------------------------------------------------------------

VOID lzw_create(PLZW_DATA lzw, HANDLE h_sour, HANDLE h_dest)

{

WORD i;

lzw->h_code = GlobalAlloc( GHND, TABLE_LEN*sizeof(WORD) );

lzw->h_prefix = GlobalAlloc( GHND, TABLE_LEN*sizeof(WORD) );

lzw->h_suffix = GlobalAlloc( GHND, TABLE_LEN*sizeof(BYTE) );

lzw->lp_code = GlobalLock( lzw->h_code );

lzw->lp_prefix = GlobalLock( lzw->h_prefix );

lzw->lp_suffix = GlobalLock( lzw->h_suffix );

lzw->code = LZW_BASE;

lzw->cur_code_len = 9;

lzw->h_sour = h_sour;

lzw->h_dest = h_dest;

memset( lzw->lp_code, 0xFFFF, TABLE_LEN*sizeof(WORD) );

}

//------------------------------------------------------------------------------

VOID lzw_destory(PLZW_DATA lzw)

{

GlobalUnlock( lzw->h_code );

GlobalUnlock( lzw->h_prefix );

GlobalUnlock( lzw->h_suffix );

GlobalFree( lzw->h_code );

GlobalFree( lzw->h_prefix );

GlobalFree( lzw->h_suffix );

}

//------------------------------------------------------------------------------

#endif

(2) fileio.h 定义了一些文件操作

#ifndef __FILEIO_H__

#define __FILEIO_H__

//------------------------------------------------------------------------------

#include <stdio.h>

#include <stdlib.h>

#include <windows.h>

//------------------------------------------------------------------------------

HANDLE file_handle(CHAR* file_name)

{

HANDLE h_file;

h_file = CreateFile(file_name,

GENERIC_READ|GENERIC_WRITE,

FILE_SHARE_READ|FILE_SHARE_WRITE,

NULL,

OPEN_ALWAYS,

0,

NULL

);

return h_file;

}

//------------------------------------------------------------------------------

WORD load_buffer(HANDLE h_sour, PBUFFER_DATA buffer) // Load file to buffer

{

DWORD ret;

ReadFile(h_sour,buffer->lp_buffer,BUFFERSIZE,&ret,NULL);

buffer->index = 0;

buffer->top = (WORD)ret;

return (WORD)ret;

}

//------------------------------------------------------------------------------

WORD empty_buffer( PLZW_DATA lzw, PBUFFER_DATA buffer)// Output buffer to file

{

DWORD ret;

if(buffer->end_flag) // The flag mark the end of decode

{

if( buffer->by_left )

{

buffer->lp_buffer[ buffer->index++ ] = (BYTE)( buffer->dw_buffer >> 32-buffer->by_left )<<(8-buffer->by_left);

}

}

WriteFile(lzw->h_dest, buffer->lp_buffer,buffer->index,&ret,NULL);

buffer->index = 0;

buffer->top = ret;

return (WORD)ret;

}

//------------------------------------------------------------------------------

#endif

(3) hash.h 定义了压缩时所用的码表操作函数,为了快速查找使用了hash算法,还有处理hash冲突的函数

#ifndef __HASH_H__

#define __HASH_H__

//------------------------------------------------------------------------------

#include <stdio.h>

#include <stdlib.h>

#include <windows.h>

//------------------------------------------------------------------------------

#define DIV TABLE_LEN

#define HASHSTEP 13 // It should bigger than 0.

//------------------------------------------------------------------------------

WORD get_hash_index( PLZW_DATA lzw )

{

DWORD tmp;

WORD result;

DWORD prefix;

DWORD suffix;

prefix = lzw->prefix;

suffix = lzw->suffix;

tmp = prefix<<8 | suffix;

result = tmp % DIV;

return result;

}

//------------------------------------------------------------------------------

WORD re_hash_index( WORD hash ) // If hash conflict occured we must recalculate

{ // hash index .

WORD result;

result = hash + HASHSTEP;

result = result % DIV;

return result;

}

//------------------------------------------------------------------------------

BOOL in_table( PLZW_DATA lzw ) // To find whether current code is already in table.

{

BOOL result;

WORD hash;

hash = get_hash_index( lzw );

if( lzw->lp_code[ hash ] == 0xFFFF )

{

result = FALSE;

}

else

{

if( lzw->lp_prefix[ hash ] == lzw->prefix &&

lzw->lp_suffix[ hash ] == lzw->suffix )

{

result = TRUE;

}

else

{

result = FALSE;

while( lzw->lp_code[ hash ] != 0xFFFF )

{

if( lzw->lp_prefix[ hash ] == lzw->prefix &&

lzw->lp_suffix[ hash ] == lzw->suffix )

{

result = TRUE;

break;

}

hash = re_hash_index( hash );

}

}

}

return result;

}

//------------------------------------------------------------------------------

WORD get_code( PLZW_DATA lzw )

{

WORD hash;

WORD code;

hash = get_hash_index( lzw );

if( lzw->lp_prefix[ hash ] == lzw->prefix &&

lzw->lp_suffix[ hash ] == lzw->suffix )

{

code = lzw->lp_code[ hash ];

}

else

{

while( lzw->lp_prefix[ hash ] != lzw->prefix ||

lzw->lp_suffix[ hash ] != lzw->suffix )

{

hash = re_hash_index( hash );

}

code = lzw->lp_code[ hash ];

}

return code;

}

//------------------------------------------------------------------------------

VOID insert_table( PLZW_DATA lzw )

{

WORD hash;

hash = get_hash_index( lzw );

if( lzw->lp_code[ hash ] == 0xFFFF )

{

lzw->lp_prefix[ hash ] = lzw->prefix;

lzw->lp_suffix[ hash ] = lzw->suffix;

lzw->lp_code[ hash ] = lzw->code;

}

else

{

while( lzw->lp_code[ hash ] != 0xFFFF )

{

hash = re_hash_index( hash );

}

lzw->lp_prefix[ hash ] = lzw->prefix;

lzw->lp_suffix[ hash ] = lzw->suffix;

lzw->lp_code[ hash ] = lzw->code;

}

}

//------------------------------------------------------------------------------

#endif

(4) encode.h 压缩程序主函数

#ifndef __ENCODE_H__

#define __ENCODE_H__

//------------------------------------------------------------------------------

#include <stdio.h>

#include <stdlib.h>

#include <windows.h>

//------------------------------------------------------------------------------

VOID output_code( DWORD code ,PBUFFER_DATA out, PLZW_DATA lzw)

{

out->dw_buffer |= code << ( 32 - out->by_left - lzw->cur_code_len );

out->by_left += lzw->cur_code_len;

while( out->by_left >= 8 )

{

if( out->index == BUFFERSIZE )

{

empty_buffer( lzw,out);

}

out->lp_buffer[ out->index++ ] = (BYTE)( out->dw_buffer >> 24 );

out->dw_buffer <<= 8;

out->by_left -= 8;

}

}

//------------------------------------------------------------------------------

VOID do_encode( PBUFFER_DATA in, PBUFFER_DATA out, PLZW_DATA lzw)

{

WORD prefix;

while( in->index != in->top )

{

if( !in_table(lzw) )

{

// current code not in code table

// then add it to table and output prefix

insert_table(lzw);

prefix = lzw->suffix;

output_code( lzw->prefix ,out ,lzw );

lzw->code++;

if( lzw->code == (WORD)1<< lzw->cur_code_len )

{

// code reached current code top(1<<cur_code_len)

// then current code length add one

lzw->cur_code_len++;

if( lzw->cur_code_len == CODE_LEN + 1 )

{

re_init_lzw( lzw );

}

}

}

else

{

// current code already in code table

// then output nothing

prefix = get_code(lzw);

}

lzw->prefix = prefix;

lzw->suffix = in->lp_buffer[ in->index++ ];

}

}

//------------------------------------------------------------------------------

VOID encode(HANDLE h_sour,HANDLE h_dest)

{

LZW_DATA lzw;

BUFFER_DATA in ;

BUFFER_DATA out;

BOOL first_run = TRUE;

lzw_create( &lzw ,h_sour,h_dest );

buffer_create( &in );

buffer_create( &out );

while( load_buffer( h_sour, &in ) )

{

if( first_run )

{// File length should be considered but here we simply

// believe file length bigger than 2 bytes.

lzw.prefix = in.lp_buffer[ in.index++ ];

lzw.suffix = in.lp_buffer[ in.index++ ];

first_run = FALSE;

}

do_encode(&in , &out, &lzw);

}

output_code(lzw.prefix, &out , &lzw);

output_code(lzw.suffix, &out , &lzw);

out.end_flag = TRUE;

empty_buffer( &lzw,&out);

lzw_destory( &lzw );

buffer_destory( &in );

buffer_destory( &out );

}

//------------------------------------------------------------------------------

#endif

(5) decode.h 解压函数主函数

#ifndef __DECODE_H__

#define __DECODE_H__

//------------------------------------------------------------------------------

#include <stdio.h>

#include <stdlib.h>

#include <windows.h>

//------------------------------------------------------------------------------

VOID out_code( WORD code ,PBUFFER_DATA buffer,PLZW_DATA lzw,PSTACK_DATA stack)

{

WORD tmp;

if( code < 0x100 )

{

stack->lp_stack[ stack->index++ ] = code;

}

else

{

stack->lp_stack[ stack->index++ ] = lzw->lp_suffix[ code ];

tmp = lzw->lp_prefix[ code ];

while( tmp > 0x100 )

{

stack->lp_stack[ stack->index++ ] = lzw->lp_suffix[ tmp ];

tmp = lzw->lp_prefix[ tmp ];

}

stack->lp_stack[ stack->index++ ] = (BYTE)tmp;

}

while( stack->index )

{

if( buffer->index == BUFFERSIZE )

{

empty_buffer(lzw,buffer);

}

buffer->lp_buffer[ buffer->index++ ] = stack->lp_stack[ --stack->index ] ;

}

}

//------------------------------------------------------------------------------

VOID insert_2_table(PLZW_DATA lzw )

{

lzw->lp_code[ lzw->code ] = lzw->code;

lzw->lp_prefix[ lzw->code ] = lzw->prefix;

lzw->lp_suffix[ lzw->code ] = lzw->suffix;

lzw->code++;

if( lzw->code == ((WORD)1<<lzw->cur_code_len)-1 )

{

lzw->cur_code_len++;

if( lzw->cur_code_len == CODE_LEN+1 )

lzw->cur_code_len = 9;

}

if(lzw->code >= 1<<CODE_LEN )

{

re_init_lzw(lzw);

}

}

//------------------------------------------------------------------------------

WORD get_next_code( PBUFFER_DATA buffer , PLZW_DATA lzw )

{

BYTE next;

WORD code;

while( buffer->by_left < lzw->cur_code_len )

{

if( buffer->index == BUFFERSIZE )

{

load_buffer( lzw->h_sour, buffer );

}

next = buffer->lp_buffer[ buffer->index++ ];

buffer->dw_buffer |= (DWORD)next << (24-buffer->by_left);

buffer->by_left += 8;

}

code = buffer->dw_buffer >> ( 32 - lzw->cur_code_len );

buffer->dw_buffer <<= lzw->cur_code_len;

buffer->by_left -= lzw->cur_code_len;

return code;

}

//------------------------------------------------------------------------------

VOID do_decode( PBUFFER_DATA in, PBUFFER_DATA out, PLZW_DATA lzw, PSTACK_DATA stack)

{

WORD code;

WORD tmp;

while( in->index != in->top )

{

code = get_next_code( in ,lzw );

if( code < 0x100 )

{

// code already in table

// then simply output the code

lzw->suffix = (BYTE)code;

}

else

{

if( code < lzw->code )

{

// code also in table

// then output code chain

tmp = lzw->lp_prefix[ code ];

while( tmp > 0x100 )

{

tmp = lzw->lp_prefix[ tmp ];

}

lzw->suffix = (BYTE)tmp;

}

else

{

// code == lzw->code

// code not in table

// add code into table

// and out put code

tmp = lzw->prefix;

while( tmp > 0x100 )

{

tmp = lzw->lp_prefix[ tmp ];

}

lzw->suffix = (BYTE)tmp;

}

}

insert_2_table( lzw );

out_code(code,out,lzw,stack);

lzw->prefix = code;

}

}

//------------------------------------------------------------------------------

VOID decode( HANDLE h_sour, HANDLE h_dest )

{

LZW_DATA lzw;

BUFFER_DATA in ;

BUFFER_DATA out;

STACK_DATA stack;

BOOL first_run;

first_run = TRUE;

lzw_create( &lzw ,h_sour,h_dest );

buffer_create( &in );

buffer_create( &out );

stack_create(&stack );

while( load_buffer( h_sour, &in ) )

{

if( first_run )

{

lzw.prefix = get_next_code( &in, &lzw );

lzw.suffix = lzw.prefix;

out_code(lzw.prefix, &out, &lzw , &stack);

first_run = FALSE;

}

do_decode(&in , &out, &lzw, &stack);

}

empty_buffer( &lzw,&out);

lzw_destory( &lzw );

buffer_destory( &in );

buffer_destory( &out );

stack_destory( &stack);

}

#endif

2 下面给出一个应用上面模块的简单例子

#include <stdio.h>

#include <stdlib.h>

//------------------------------------------------------------------------------

#include "lzw.h"

#include "hash.h"

#include "fileio.h"

#include "encode.h"

#include "decode.h"

//------------------------------------------------------------------------------

HANDLE h_file_sour;

HANDLE h_file_dest;

HANDLE h_file;

CHAR* file_name_in = "d:\\code.c";

CHAR* file_name_out= "d:\\encode.e";

CHAR* file_name = "d:\\decode.d";

//------------------------------------------------------------------------------

int main(int argc, char *argv[])

{

h_file_sour = file_handle(file_name_in);

h_file_dest = file_handle(file_name_out);

h_file = file_handle(file_name);

encode(h_file_sour, h_file_dest);

// decode(h_file_dest,h_file);

CloseHandle(h_file_sour);

CloseHandle(h_file_dest);

CloseHandle(h_file);

return 0;

}

3 后语

之前研究gif文件格式时偶然接触了lzw压缩算法,于是就想自己动手实现。从一开始看人家的原码,然后跟着模仿,到现在用自己的语言表达出来,从理解原理到代码的实现花费了不少时间与精力,但是真正的快乐也就在这里,现在把她拿出来跟大家分享也就是分享快乐。

 
 
 
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